Culling Badgers to Protect Cows

The incidence of bovine tuberculosis (TB) in British cattle has been increasing since the 1980s, despite a program of testing cattle and slaughtering those showing evidence of exposure to the bacteria (Mycobacterium bovis) which cause the disease. Transmission from wild badgers has made an important contribution to the incidence of infection in cattle herds, and for this reason various approaches to badger culling have been undertaken in efforts to reduce disease in cattle.

A large field experiment, the so-called Randomised Badger Culling Trial (1998-2006) undertaken in south-west England, scientifically evaluated the impacts of two forms of badger culling, compared to no badger culling. It found that repeated widespread culling of badgers could significantly reduce disease risk among cattle herds on culled land but with the unintended consequence that cattle herds on nearby land experienced greater disease risk during the culling period. Furthermore, localised culls were found to increase disease risk among cattle herds.

These results have been cited by different interest groups to support diametrically opposed ways forward. Those against the culling cite: the increased risks to nearby cattle herds; the relatively high costs of culling as carried out in the Trial (surveying, trapping and shooting trapped badgers) compared to the economic savings expected due to bovine TB incidents prevented; and of course, the number of badgers that would be culled in the name of disease control.

Those in favour of culling cite the clear evidence that large, coordinated and repeated badger culls reduced overall disease risks in cattle, as well as pointing out that TB incidence in cattle is increasing in both England and Wales. The proposed policies differ in England and Wales, a consequence of devolved decision-making on animal health.

The Welsh public awaits a decision on whether to go ahead with the proposed single culling area of 288 sq-km which includes a section of sea-boundary to reduce the number of herds exposed to increased risks on land surrounding the proposed cull. The proposed culling method would be similar to that used in the Trial in that it involves repeatedly surveying, trapping and shooting trapped badgers. However, an additional measure has been included in the proposals in which land owners must not deny access to their land for culling.

In England, groups of farmers and land owners have been told that they may apply for licenses to cull badgers provided that they meet specific criteria. These include that the area is large (150 sq-km or more), that there is access for culling on at least 70% of the area and that the culling will be repeated annually for at least 4 years. Critically, farmers must pay for the costs of culling, with the government limiting its economic contribution to the evaluation of license applications and subsequent monitoring of culling activities once they have been licensed. To reduce culling costs, farmers will be allowed to include the shooting of free-ranging badgers, a method which the government has calculated will be cheaper than the shooting of badgers caught in traps. This change has raised both questions of health and safety, animal welfare (in case badgers or non-target species were wounded rather than killed immediately) and uncertainty as to whether this method of culling would deliver the same impacts on cattle disease risks as observed in the large-scale trial.

Controversy and debate are bound to continue. The challenge for scientists will be how the impacts of a one-off Welsh cull or what may be up to 10 English culls licensed each year can be estimated sufficiently well to inform those debates.

About Professor Christl A Donnelly

Christl A. Donnelly is professor of statistical epidemiology at the MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London. Prof Donnelly was the Deputy Chair of the Independent Scientific Group on Cattle TB which designed, oversaw, analyzed and interpreted the Randomised Badger Culling Trial (1998-2006). She has advised stakeholders and policy makers on the control of influenza, SARS, bovine TB, foot and mouth disease, bovine spongiform encephalopathy and new variant Creutzfeldt-Jakob Disease (vCJD). Several of her bovine TB research projects have been funded by the UK Department for Environment, Food and Rural Affairs.